Integrated circuits typically contain a large number of semiconductor devices. Manufacturers of the integrated circuits often wish to decrease the size of the integrated circuits, which allows more circuitry to be placed within the same physical area of a circuit. To help decrease the size of the integrated circuits, the manufacturers may place the semiconductor devices closer together in the integrated circuits. One problem is that capacitance between the semiconductor devices typically increases as the space between the semiconductor devices decreases. The increased capacitance between the semiconductor devices can interfere with the operation of the semiconductor devices and with the operation of the integrated circuits.
One approach to decreasing the capacitance between the semiconductor devices involves decreasing the thickness of the semiconductor devices. For example, the manufacturers may reduce the thickness of gates used in transistors. The capacitance between the semiconductor devices is typically proportional to the cross-sectional area of the semiconductor devices. Because thinner semiconductor devices have less cross-sectional area, the capacitance between the semiconductor devices typically decreases. A problem with this approach is that difficulty may be encountered in maintaining the operation of the semiconductor devices. As the semiconductor devices become thinner, the reduced size of the devices may interfere with the ability of the devices to conduct. Eventually, the reduced thickness of the semiconductor devices may prevent the devices from conducting, and the semiconductor devices in the integrated circuits can fail.
Another approach to decreasing the capacitance between the semiconductor devices involves lowering the dielectric constant (K) of the insulating material between the devices. For example, oxide may be used as an insulating material in an integrated circuit, and oxide typically has a dielectric constant of approximately four. The capacitance between the semiconductor devices is typically proportional to the dielectric constant of the insulating material. As a result, lowering the dielectric constant of the insulating material reduces the capacitance between the semiconductor devices. A problem with this approach is that, as manufacturers place the semiconductor devices closer together, the dielectric constant of the insulating material may still be high enough to allow the formation of an appreciable amount of capacitance in the integrated circuit. Also, the insulating material may suffer from contamination, such as by metal ions like sodium, that interferes with the operation of the integrated circuit.